In recent years, data communication traffic has steadily been increasing, and in response to this, for example, in devices, such as IC cards and mobile phone units, communications in the radio-frequency range, such as the microwave range or the millimeter wave range, have become widely used. Accordingly, there has been a demand for a radio-frequency printed circuit board which has a small transmission loss when used in the radio-frequency range.
In a commonly used printed circuit board, the transmission rate V and the transmission loss ad satisfy the relationships (expressions (1) and (2)) below, where εr is the relative dielectric constant of the dielectric layer, f is the frequency, and tan δ is the dielectric loss tangent.
                    [                  Expression          ⁢                                          ⁢          1                ]                                                            V        ∝                  1                                    ɛ              ⁢                                                          ⁢              r                                                          (        1        )                                [                  Expression          ⁢                                          ⁢          2                ]                                                                      α          ⁢                                          ⁢          d                ∝                  f          ×                                    ɛ              ⁢                                                          ⁢              r                                ×          tan          ⁢                                          ⁢          δ                                    (        2        )            
That is, in order to increase the transmission rate V and decrease the transmission loss αd, it is required to decrease the relative dielectric constant εr of the dielectric layer. Therefore, it has been proposed to use, as the material for dielectric layers, fluororesins, such as polytetrafluoroethylene (PTFE), a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), an ethylene-tetrafluoroethylene copolymer (ETFE), and polyvinylidene fluoride (PVdF), (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-7466 and Japanese Patent No. 4296250).